Always use heavy/pro gear, or keep alternatives?

I'm curious, for those photographers who have heavy (pro) equipment - do you always use that or do you have alternatives?

The reason I ask is that I just bought a 70-200mm 2.8 lens, and obviously it has some good weight (1.5kg-ish). I have a 70-210mm f4 lens that I was going to dump. However the f4 shoots great shots (slightly stopped down) and is half the weight and much less size.

So on one hand, it seems silly to have both lenses. On the other hand, the 70-210mm isn't worth much ($150), and if it means I can carry way less when I don't 'need' the 2.8 - it's a nice alternative.